Power supply circuit arrangement



Jan.l6, 1970 M. J. VADROT 3,488,519 POWER SUPPLY CIRCUIT ARRANGEMBNT I Filed aime 24. '196e 5 sheets-sheet 2 M. J. VADROT Pom-:R SUPPLY CIRCUIT ARRANGBMENT Jan. 6, 1970 3 Sheets-Sheet 3 Filed June 24, 196s United States Patent Gti ice 3,488,519 POWER SUPPLY CIRCUIT ARRANGEMENT Michel Jacques Vadrot, Paris, France, assignor to Societe Industrielle Bull-General Electric (Societe Anonyme), Paris, France Filed June 24, 1966, Ser. No. 560,138 Claims priority, applicationzFrance, July 27, 1965,

26,09 Int. Cl. Hosk 17/02 U.S. Cl. 307-246 10 Claims ABSTRACT F THE DISCLOSURE This invention relates to a power supply circuit arrangement for the operation of a fairly large number of electromagnets, which may be actuated at various moments during an operating cycle.

The problem solved by the invention may arise mainly in the case of a high-speed printing machine provided with a type drum. It is known that the printing can be carried out in the course of the striking period, which is a fraction of a printing cycle, which corresponds to one revolution of the drum. The various ch-aracters are successively printed as the series of aligned characters on the drum travel past a series of printing hammers. The electromagnets which actuate the hammers must be selectively energised at the desired instants during the striking period. The remainder of the printing cycle, or skip period, may be used to effect the paper feed, also called the paper skip.

In so-called cyclic printing machines, printing is carried out in each printing cycle. In other, so-called acyclic printing machines, which operate under the control of the central unit of a data processer, for example, the printing of a line of type is not effected in each printing cycle, either because the paper feed lasts longer than a skip period or because various operations are introduced between two successive printing operations.

It is known that in some printing machines comprising a type drum a separate capacitor is relied upon to supply a constantly uniform energy to each electromagnet effecting the actuation of a striker hammer, on the basis of the relation Q=CV, C and V being assumed to be constant. Since the tolerances in regard to the capacitances of the various printing positions may be readily compensated for by adjustable electric or mechanical means, only variations of V (charge voltage of the capacitors) can influence the response time of the striking mechanisms and consequently can have repercussions upon the alignment of the printed characters. Now, the character striking period extends over a considerable part of a revolution, for example 85 ms. (milliseconds) of a printing cycle lasting 100 ms. Even if a regulated voltage supply is provided to charge the capacitors, it is not possible to be sure that this voltage V, which exists at a given instant, will be exactly the same throughout the striking period, for example 50 ms. later.

In an earlier device of this type, the recharging of each of the capacitors takes place automatically immediately after the associated electromagnet has been energised by 3,488,519 Patented Jan. 6, 1970 2 its discharge current. It is obvious that the response time of an electromagnet may then vary in accordance with the value of the charge voltage V of the capacitors at the precise instant when the discharge of the corresponding Capacitor is produced by the closing of an associated switch.

The essential principle upon which the invention is based consists in effecting the simultaneous recharging of all the capacitors associated with the actuating electromagnets, at a predetermined instant before the hammer striking period. In this way, it is certain that all the capacitors are charged at the same voltage before the printing of each line of characters. Thus, the most important cause of bad alignment of the characters is eliminated. As an accessory, it is possible to employ a unit for the supply of rectified voltage which does not require regulation.

Consequently, in accordance with the invention, in a high-speed printing machine comprising a type drum, in which there is provided for each of the printing locations a hammer actuating electromagnet, which is to be energised by a constant energy at an instant during the striking period of a printing cycle, this instant varying with the character to be printed, a printing capacitor which is to be charged at a predetermined Voltage (-Vz) during the skip period of a printing cycle, and. a diode in series with the capacitor, there is provided an energy-supplying arrangement comprising: a non-regulated voltage source comprising a transformer and a rectier supplying a unidirectional voltage (-Vl) higher than the said predetermined voltage, a thyratron switch connected between the non-regulated voltage (-Vl) and a common terminal connected to all the diodes associated with the printing capacitors, a control circuit adapted to close the switch when it receives a control pulse at the beginning of a skip period, and a transistorised voltage-comparing device connected to compare a derived voltage which varies during the charging of the printing capacitors with a xed reference voltage and adapted to effect the opening of the switch when the voltage across the terminals of the printing capacitors reaches the said predetermined voltage, before the end of the said skip period.

With a view to its application to an acyclic printing machine, the energy-supplying arrangement comprises elements by means of which the currents which tend to discharge the printing capacitors are compensated for during the variable time between the charging period, which coincides with the skip period, and the beginning of the striking period in the course of which a line of characters is printed. In this case, there is also provided a discharge-authorising device which is operative only in the course of an effective striking period.

An additional advantage of this energy-supplying arrangement is that it permits of solving to advantage the problem of the change-over of the printing elements.

For a better understanding of the invention and to show how it may be carried into effect, the same will now be described, by way of example with reference to the accompanying drawings, in which:

FIGURE 1 is a basic diagram of an energy-supplying arrangement according to the invention, and

FIGURES 2A and 2B (which should be joined along the lines XX) represent a detailed electric circuit diagram of this circuit arrangement.

The basic diagram of FIGURE l represents an energysupplying arrangement intended to be incorporated in an acyclic printing machine controlled by the central unit of a data processer.

There has been shown to the right of the line YY in this ligure a block 10 which represents the printing elements included in the printing machine. There may be seen to the right of the line YY in FIGURE 2B the composition of such a printing element. The latter comprises a hammer-actuating electromagnet EAM, the winding of which has been drawn, a printing capacitor CI, a switching transistor T7, a fusible link F3, `and a diode D7, the whole being connected as shown between the conductors 12 and 15. If the printing machine is provided with 136 printing locations, there exist 136 parallel-connected identical printing elements. v

Normally, each of the transistors such as T'7 is nonconductive because a positive voltage is applied to each of the terminals 56, which is connected to the base of the transistor T7. At the end of a charging period, each of the capacitors CI must be charged at the voltage existing between the conductors 12 and 15, i.e. -48 volts, neglecting the voltage drop across the terminals of the diodes D7, At the beginning of an eective striking period, the voltage along the conductor may rapidly decrease or be brought to a much lower value than 48 volts, at which voltage the non-selected printing capacitors may remain charged, the diodes D7 then being biassed in the sense of high inverse resistance. If, for example, the drum carries 64 series of different types, the striking period is divided into 64 striking moments. At each of these moments, one or more printing elements may be selected by the application of a negative pulse to the corresponding terminal 56. The corresponding transistor T7 then becomes highly conductive and its internal resistance becomes negligible. The capacitor CI then discharges into the winding of the electromagnet EAM, which actuates the associated printing hammer.

Referring again to FIGURE 1, the supply system comprises a non-regulated unidirectional-voltage source 11. This source comprises a transformer-rectiier-capacitor set supplied with the mains 220-volts 50-c./s. alternating current, and supplying at its output a filtered unidirectional voltage which is nominally of 80 volts, but which may vary from 70 to 90 volts.rThus, with the conductor 12 at a potential of O volt, the potential of the conductor 13 is normally of -80 volts.

A charge switch device 14 is connected between the conductor 13 and the conductor 15, which is in turn connected to all the printing elements, as has been seen. At the beginning of a charging period, a control pulse is applied to the terminal 16 of the switch 14 to close it and to start the recharging of the printing capacitors. This switch is under the control of a voltage comparator 17. This device is adapted to compare a variable voltage derived from an adjustable tap of the voltage divider 18 with a iirst xed reference voltage (not shown in this figure). The voltage divider 18 is connected between the conductors 12 and 15. The voltage derived from the voltage divider is so adjusted that when the potential of the conductor 15 reaches -48 volts during the charging of the capacitors, the comparator 17 supplies to the switch 14 a signal which has the effect of opening it and therefore of interrupting the charging of all the printing capacitors.

It is known that during the printing of a line of characters, the number of actuated printing elements is essentially variable. Considering the extreme cases as possible, it may be assumed, with the example already mentioned, that in the course of a striking period the number of printing capacitors which have been discharged may vary from l to 136. In order to regularise the charging duration of the capacitors, at least to some extent, there is provided a device 19 which simulates a certain number of imaginary printing elements. The said device is essentially a capacitor connected in parallel between the conductors 12 and 15, and the capacitance of which is equivalent to that of ten printing capacitors, for example, Of course, this capacitor must be discharged immediately the charging period has ended.

Since the interval of time between a charging period of the capacitors and the effective striking period is essentially variable in the case of an acyclic printing machine, means are provided to maintain the capacitors charged at the nominal charging voltage even if this interval lasts several printing cycles. These means consist of a device 20 supplying a reference voltage, associated with a resistor 21, these two members being connected in series between the conductors 12 and 13, and their junction point being connected to the conductor 15. The device 20 may be a simple Zener diode.

In addition, there is provided a discharge-authorising device 22 which is connected between the conductors 12 and 15. The control circuits of the machine supply at the terminal 23 a signal which lasts throughout a striking period in the course of which a printing is desired. The effect of this signal is that the device 20 is shunted during this time by a resistance of relatively low value, whereby the potential of the conductor 15 is brought to a value much lower than -48 volts, for example of *14 volts, so that the printing capacitors may be individually discharged.

FIGURES 2A and 2B, which may be connected along the lines XX, supply particulars regarding the circuit arrangement provided and enable certain details concerning their operation to be given.

The voltage source 11, FIGURE 2A, which has to supply a non-regulated unidirectional voltage, is very simple. It comprises a transformer 24, a full-wave rectifier set 25, composed of four silicon diodes connected in bridge, and a ltering capacitor CF. The latter may in fact be a battery of capacitors, having a total capacitance of 30 mf. (millifarads), for example. This assembly is very convention-al and its only requirement is that the Ohmic resistance of the windings of the transformer should be low. There is available at the output terminals 26, 27 a unidirectional voltage of volts, which may vary between 70 and 90 volts. For example, the zero voltage iS that of the termin-al 26, which is connected to earth and to the conductor 12. The potential of -80 volts is available at the terminal 27, which is connected to the conductor 13.

The element 20 consists of a Zener diode DZ1, which is connected in series with the resistor 21. The said Zener diode is, for example, of the type 1N3330B, which has across its terminals a voltage drop of 48 volts when it is traversed by the current 'admitted by the 68-ohm resistor 21.

The discharge-authorising device 22 is composed essentially of the transistors T1, T2. One end of the resistors 28, 29 is connected to a terminal of a unidirectional-voltage source (not shown) which supplies a voltage -i-V3 of +10 volts. One end of the resistors 30, 31 is connected to another unidirectional voltage source (not shown) which supplies a voltage V2 of -12 volts. The resistor 32, of l2 ohms, is connected between the collector of the transistor T2 and the conductor 15. The diode D1 opposes an excessive positive bias of the base of T2.

In the absence of the discharge-authorising signal, i.e. outside an effective striking period, the potential applied to the terminal 23 is equal to that of earth. The current flowing through the resistors 28 and 33 renders the base of T1 more positive than its emitter, so that the transistors T1 and T2 are rendered non-conductive. At all times outside a charging period, the potential of the conductor 15 is -48 volts, as already stated.

In -a-n elfective striking period, for example of ms., the control circuits of the machine supply the dischargeauthorising signal, which brings the terminal 23 to a potential of l2 volts. It is clear that the transistors T1 and T2 then become highly conductive, the practical result of which is that the resistor 32 is placed in parallel with the diode DZ1. The current flowing through the latter becomes insignificant and the potential of the conductor 15, which is determined by the voltage divider 32, 21, remains lat about -14 volts during the striking period.

In the charging switch assembly 14, FIGURE 2B, the main element consists of a solid thyratron THl which may be of the type TC10. The anode of the latter is connected to the conductor 15 through the resistor 51, the fusible link F2 and the diode D4. The ends of the secondary winding of the transformer 55 are connected to the control electrode and to the cathode of the thyratron TH1. The winding of an inductor L is connected between the cathode of TH1 and the conductor 13.

A current amplifier st-age is provided which comprises the transistor T6 and the resistors 42-44, connectedas shown. The collector of T6 is connected to the source supplying the voltage-V2 through the primary windingof the transformer 55 and the limiting resistor 49. Outside the charging periods, the lpotential applied to the terminal 16 by the control circuits of the machine is earth potential, so that the transistor T6 is non-conductive. lAt the beginning of a charging period, which coincides with the skip period of a printing cycle, the terminal 16 receives `a negative pulse of a minimum duration of 20 microseconds and of an amplitude of -12 volts. Since the transistor T6 becomes conductive, a current pulse is supplied by the transformer 55 to the control electrode of the thyratron TH1, which becomes conductive and is equivalent to a closed switch. The function of the second solid thyratron TH2 is to effect, through the capacitor C4, the disconnection of the thyratron TH1. The anode of TH2 is connected to the conductor 12 and thus to earth through the resistor 50 and the fusible link F1. The cathodeof TH2 is directly connected to the upper end of the winding of the inductor L. The ends of the secondary winding of the second transformer 54 are connected to the control electrode and to the cathode of TH2. TH2 is brought into the conductive state under the control of the volt-age comparator 17, which will now be considered.

In the present embodiment, the voltage comparator is formed of a Schmitt trigger circuit composed of transistors T3 and T4 of NPN type, and of the resistors and capacitors usually employed in this type of circuit. The resistor 41 is common to the emitters of T3 and T4. The base of T3 is connected to the base of the collector T4 vthrough the resistor 39 yand the capacitor C2.

Of the voltages to be compared, a iirst xed reference voltage Vr is available at the junction between two Zener diodes DZ2 and D23 connected in series and a resistor 34, these members being in series between the cOnductors 12 and 13. The capacitor C1 serves to decouple the diodes DZZ and DZ3. When the potential V1 of the conductor 13 is -80 volts, the Said reference voltage is about -16 volts. The other voltage to be compared, which is variable, is applied to the base of T4. It is derived from the adjustable tap 57 of the voltage divider 18. The latter comprises, in this order, the resistor 45, the potentiometer l46, the resistor 47 shunted by the capacitor C3 and the diode D2 the cathode of which is connected to the conductor 15.

The amplifier transistor T5 of PNP type has its base connected to the junction point of the resistors 35 and 36. Its collector is connected to the source supplying the voltarge V2 through the primary winding of the transformer 54 and the limiting resistor 48.

The adjustable tap 57 of the potentiometer 46 is so adjusted that when the potential of the conductor 15, i.e., substantially that of the lower plates of the capacitors CI, is -48 volts, only the transistor T4 is conductive, the transistors T3 and T5 being non-conductive. The values of the resistors 39 and 40 are so chosen that with T4 conductive the base of T3 is slightly negative in relation to its emitter. On the other hand, the resistors 35, 37 form a voltage divider which, in the absence of collector current of T3, renders the base of T5 positive.

In the device 19 simulating a certain number of printing elements, the capacitor C5 has its lower plate connected to the anode of the thyratron TH1 through the diode D3, the fusible link F2 and the resistor 51. The capacitor C5 may therefore receive a charge each time that TH1 is conductive. The resistor 52 is connected to permit the discharge of the capacitor C5 as soon as the switch is re-opened. The time constant of the discharge circuit thus formed is 32 ms., in order that C5 may be completely or almost completely discharged at the end of a time equivalent to one striking period, i.e., ms. as previously indicated.

Another time-constant circuit is formed of the capacitor C6 and of the resistor 53. It has the object of preventing the potential of the junction .B from returning too rapidly to the zero voltage of earth when the thyratron TH1 is cut off. The diode D5 is provided by way of precaution to prevent the potential of the junction B' from temporarily exceeding that of earth.

By way of example, there are indicated in the following a number of values of the components which have proved satisfactory in the development.

Resistors:

34 ohms 680 35 ..kil0hms 1.5 36 do 2.7 37 do 27 38 do 2.7 39 ohms-- 560 40 kilohms 8.2 41 ohms 220 42 kilohms-- 2.7 43 do 2.2 44 do 10 45 do 3.9 46 do 2.2 47 do 10 48 ohms-.. 100 49 do 100 50 do 8.2 51 do 0.3 52 do 16 53 do 470 Inductor L microhenrys 60 Capacitors:

C1 millifarad-.. 0.1 C2 picofarads 680 C3 nan0farads 2.7 C4 -microfarads 50 C5 do 2 C6 do 16 CI do 0.2

The operation will be examined from the end of a striking period, in the course of which printing capacitors CI have been discharged, the number of the latter being variable between Zero and 136. It is to be noted that the duration of each of the selecting pulses applied to one of the terminals 56 (FIGURE 2B) is so limited that the printing capacitor CI concerned is not completely discharged, in order that the residual voltage may be approximately equal to the voltage -Vz of the conductor 15, i.e., -14 volts, defined by the voltage divider formed of the resistors of T2, 32 and 21 (FIGURE 2A). On the other han-d, the capacitor C6 is completely discharged at this instant, and the capacitor C5 is also almost completely discharged.

During the immediately following charging period, which lasts 15 ms., a charge control pulse is received by the terminal 16, for example 0.5 ms. after the end of the discharge-authorising signal received 'by the terminal 23. As already stated, the effect of this pulse is to render conductive the transistor T6 and the thyratron TH1, which will remain conductive after the end of this pulse.

Since the potentials of the points A, LB and B are substantially zero at this instant, the current owing through TH1 serves tirst of all to charge the capacitors C4, C5 and C6. However, the inductor L momentarily opposes a too sudden change of the current flowing through it and on the other hand the charging current is limited by the ohmic resistances of the circuit, the greater part of which is formed by the resistor 51. The potential at the point B falls rapidly, while the voltage in absolute value at the point B increases exponentially with the charge of C and C6. As soon as the potential at the point B becomes lower than the potential -Vz of the conductor 15, whlch has not been able to change substantially, the diode D4 becomes biased in the forward direction, as also do the diodes D7, the printing capacitors of which are discharged. The latter then begin to charge and the potential -Vz of the conductor changes towards the potential of the conductor 13, i.e., -80 volts, more or less rapidly in accordance with the total capacitance of the capacitors to be recharged. v

It will be observed that the capacitance of `C5 1s equivalent to that of ten printing capacitors CI. Excesslve changes in the charging duration are thus avoided. The charging of the capacitors will be stopped when the potentential of the common conductor 15 reaches the rated charging voltage, i.e. -48 volts, this voltage being defined by the diode DZ1. If there is only one capacitor CI t0 be recharged, the charging is terminated at the end of about 0.8 ms., and if there were 136 capacitors CI to be recharged, the charging would take about 14 ms. At the end of the charging, the current flowing through TH1 has considerably reduced and the capacitor C4 is charged with at least about fifty volts.

At the beginning of the charging period, the transistor T4 in the voltage comparator was oversaturated, since the potential of the conductor 15 was only -14 volts. When the voltage between the conductors 12 and 15 increases in the course of the charging of the capacitors, the voltage at the slider 57 of the potentiometer 46 increases in proportion in relation to the conductor 12. This voltage change in the negative sense has the effect of reducing the base current of T4 without first of all varying its collector current. A time arrives when the said base current has further reduced and the transistor T4 leaves the saturated state while still being conductive. The positive voltage between the collector and the emitter of T4 then increases substantially and since this voltage change in the positive direction is fairly rapid, it is transmitted by the capacitor C2 to the base of the transistor T3. Owing to the wellknown cumulative effect, the conduction of T3 brings about the momentary cutting-off of the transistor T4. Since the collector current of T3 must emanate for the greater part from the base current of T5, the latter rapidly becomes conductive. It is required to supply a current pulse having a minimum duration of microseconds. This pulse is transmitted by the transformer 54 to the control electrode of the second thyratron TH2.

As soon as the latter becomes conductive, the temporarily supplied current increase gives rise to a countervoltage across the terminals of the inductor L, taking an oscillatory form. On the other hand, the voltagel drop at the point A is transmitted by the capacitor C4 to the anode of TH1. The voltage between the points B and C is rapidly cancelled out, so that the first thyratron TH1 again becomes non-conductive and the charging of the capacitors is interrupted.

In the course of the oscillatory phenomenon, the period of which is determined by the values of L, C4 and 51, the potential of the point C increases, while that of the point A decreases. A time arrives when the voltage between the points A and C is cancelled out, whereby the second thyratron TH2 is brought to the non-conductive state. The values chosen for L, C4 and 51 are such that the duration of the conduction of TH2 is about 200 microseconds.

If the capacitor C6 and the resistor 53 were not present, the potential at the point B would rise rapidly towards earth potential as soon as the thyratron TH1 was cut off, so that the thyratron TH1 might be retriggered. It is clear that this effect is prevented by the circuit C6-53, the time constant of which is 8 ms.

Owing to the diode D3, the conductor 15 can be brought from -48 volts to -14 volts at the beginning of a striking period immediately succeeding the charging Period if the printing is carried out in the same printing cycle as the chargingl of the capacitors. In this case also, the presence of the capacitor C6 does not substantially interfere with the operation, by reason of its relatively low capacitance.

The diode D4 enables C5, C6 and the capacitors CI to charge concurrently during the charging period where the diode is forward biased. On the contrary, after a charging period, the diode D4 becomes nonconductive since conductor 15 remains at -48 volts, and thus the capacitors C5 and C6 can begin to discharge immediately after the interruption of the charging current. In addition, the diode D4 pen/ents the charging of C5 and C6 when voltage is applied to the energy-supplying arrangement.

In the voltage divider 18, the function of the capacitor C3 is as follows. It is effective only when the number of capacitors to be recharged is very small. Thus, the voltage change of the conductor 15 is relatively the most rapid. In this case, the capacitor C3 represents a relatively low impedance which has the effect of raising the ratio of the voltage transmitted to the base T4 as compared with the momentary voltage of the conductor 15. Therefore, T4 is cut off a little earlier and the charging is interrupted before the charging voltage of the capacitors has reached -48 volts. Consequently, an effect of accumulation of the charges at the capacitors previously not discharged is avoided.

In cases where the printing of a line of type is effected only during one of the printing cycles succeeding the charging period of the printing capacitors, the charging voltage of the latter must be maintained substantially at the above-indicated rated value. This function is performed by the resistor 21 and the Zener diode DZ1, FIG- URE 2A. It is necessary to compensate during an indeterminate time, for the currents tending to discharge the printing capacitors, of the electro-chemical type, namely the leakage currents of these capacitors and those flowing through the switching transistors T7, the resistance of which is not infinite, even in the nonconductive state. The said Zener diode is so chosen that the voltage drop across its terminals is not excessively reduced if the current flowing through it is reduced from 0.2 ampere, which is the mean value of the compensating current.

It is to be noted that the voltage comparator 17 could be constructed in any other form. Instead of the Schmitt trigger including the transistors T3, T4, there could be provided another amplitude-discriminating device followed by a monostable trigger circuit, which devices are well known in the present art. However, this solution would be more costly since it would necessitate a larger number of transistors.

It may be seen that, owing to the co-operation of the described devices, the essential object of the invention is fully achieved, namely to ensure the same charging voltage for all the printing capacitors at the beginning of an effective striking period, regardless of the number of capacitors which has had to be recharged and regardless of the time elapsing between the charging period and the said effective striking period.

The only important variation of the charging voltage of the printing capacitors arises out of the fact that some of the latter are discharged at the beginning and others at the end of a striking period during which the voltage at the conductor 15 obviously can no longer be maintained at -48 volts. The change resulting therefrom does not exceed or 0.4 volt, the effect of which is an admissible misalignment of the printed characters of one line of characters. All the other causes of voltage change, such as those resulting from the voltage fluctuations of the non-regulated source 11, are of no importance in regard to the alignment of the characters, since they can only take effect from one line of printed characters t0 another.

The invention may also be applied to a cyclic printing machine in which each printing cycle is composed of a charging period followed by an effective striking period. Certain devices, namely the reference voltage device 20, the resistor 21 and the discharge-authorising device 22, may then be omitted, because the charging voltage of the printing capacitors no longer has to be maintained and the device 22 becomes unnecessary. The operation of the remaining devices in the assembly is the same as has previously been described.

It is to be noted that the voltages -|-V3 and -V2 must be appropriately regulated. Since the current strengths required at the corresponding voltages are relatively low, it is possible to use those which generally exist either in the supply cubicle of the printing machine or in the associated data processor.

Although the diodes D22, DZ3 and the resistor 3-4 may be replaced by another regulated voltage source to supply the reference voltage -Vr, the solution adoptedhas the advantage of being inexpensive and that this voltage -Vr exists only during the time when the energy-Supply arrangement is being set in action.

Further modifications and adaptations are obviously within the scope of the person skilled in the art.

What is claimed is:

1. In a printing machine with a type-bearing drum, comprising for each printing position, a hammer-actuating electromagnet which may be energized at a variable moment of a printing cycle through the discharge of an associated print capacitor, which should be recharged during a skip period in the same cycle and which is one of a plurality of capacitors, a power supply circuit arrangement comprising a source of unregulated D-C voltage, a thyratron switching device, circuit means including conductors arranged to connect one plate of each capacitor f said plurality of capacitors to a first terminal of said source, a plurality of diodes arranged to connect separately the other plate of each capacitor of said plurality of capacitors to a first terminal of said switching device control means coupled to said switching device to initiate conduction of said switching device at a fixed moment of a printing cycle, a second terminal of said source which supplies an unregulated voltage greater than a predetermined voltage, said switching device including a first solid thyratron having a cathode terminal, an anode terminal and a control terminal, an inductor connecting the cathode terminal of said thyratron to said second terminal of said source, a common conductor connected to all of said diodes and through a resistor to the anode terminal of said thyratron, a reference voltage supply means supplying a fixed reference voltage, and a voltage comparator device connected to Compare a voltage derived from the voltage of said common conductor, varying during charging of said capacitors, with said fixed reference voltage for supplying .a control signal to said switching device, which signal cuts off said thyratron by a reactive action from said inductor, in order to interrupt the charging of said plurality of capacitors whenever the voltage of said common conductor becomes equal to said predetermined voltage.

2. A circuit arrangement as claimed in claim 1, wherein said control means includes a control transformer having the secondary winding thereof coupled between said cathode terminal and said control terminal.

3. A circuit arrangement as claimed in claim 1, wherein said switching device further comprises a second solid thyratron whose anode `is Acapacitively coupled to the anode of said first thyratron, and wherein said comparator device includes a resistive voltage divider connected between said first terminal and said common conductor and having a settable tap, a Schmitt trigger circuit with two transistors, one having its base connected to said tap, and circuit means coupled to said trigger circuit and including a transformer to cause the conduction of said second thyratron.

4. A circuit arrangement as claimed in claim 3 wherein a dummy capacitor unit is connected on the one hand to said first terminal and on the other hand through an isolating diode to said common conductor and through said resistor to the anode of said first thyratron, said dummy capacitor unit including a resistor parallel connected to a capacitor whose capacity is equivalent to that of several of said print capacitors.

5. In a printing machine with a type bearing drum comprising for each printing position, a hammer actuating electromagnet which may be energized at a variable moment of a printing cycle through the discharge of an associated print capacitor, which should be charged at a predetermined voltage during a prior skip period in the same cycle or in another cycle prior to said printing cycle, and which is one of a plurality of capacitors, a power supply circuit arrangement comprising a source of unregulated D-C voltage, a thyratron switching device, circuit means including conductors arranged to connect one plate of each of said capacitors to a first terminal of said source and, a plurality of diodes arranged to connect separately the other plate of each Capacitor of said plurality of capacitors to a first terminal of said switching device, control means coupled to said switching device to initiate the conduction of said switching device at a fixed moment of a printing cycle, a second terminal of said source which supplies an unregulated voltage greater than said predetermined voltage, said switching device including a first solid thyratron having a cathode terminal of said source, a common conductor connected the cathode terminal of said thyratron to said second terminal of said siurce, a common conductor connected to all of said diodes and through a resistor to the anode terminal of said thyratron, a reference voltage supply means supplying a fixed reference voltage, and a voltage comparator device adapted and connected to compare a voltage derived from the voltage of said common conductor, varying during charging of said] capacitors, with said fixed reference voltage and for supplying a control signal to said switching device, which signal cuts off said thyratron by a reactive action from said inductor, in order to interrupt the charging of said print capacitors as soon as the voltage of said common conductor becomes equal to said predetermined voltage.

6. A circuit arrangement as claimed in claim 5, wherein said control means includes a control transformer having the secondary thereof coupled between said cathode terminal and said control terminal.

7. A circuit arrangement as claimed in claim 5, wherein said switching device further comprises a second solid thyratron whose anode is capacitively coupled to the anode of said first thyratron, and wherein. said comparator device includes a resistive voltage divider connected between said first terminal and said common conductor and having a settable tap, a Schmitt trigger circuit with two transistors, one having its base connected] to said tap, and circuit means coupled to said trigger circuit and including a transformer to cause the conduction of said second thyratron.

8. A circuit arrangement as claimed in claim 7, wherein a dummy capacitor unit is connected Ion the one hand to said first terminal and on the other hand through an isolating diode to said common conductor and through said resistor to the anode of said first thyratron, said dummy capacitor unit including a resistor parallel connected to a capacitor whose capacity is equivalent to that of several of said print capacitors.

9. A circuit arrangement as claimed in claim 7, including a Zener diode with an electrode connected to said first terminal of said supply source, and a resistor with an electrode connected to said second terminal of said supply source, the other electrode of said diode and the other end of said resistor being connected together to said common conductor, said diode and resistor being so chosen as to maintain said common conductor at said predetermined voltage in the time intervals between the periods the charge and discharge of said print capacitors take place.

10. In a printing machine witha type bearing drum comprising for each printing position, a hammer actuating electromagnet which may be energized at a variable moment of a printing cycle through the discharge of an associated print capacitor, which should be charged at a predetermined voltage during a prior skip period in the same cycle or in another cycle prior to said printing cycle, and which is one of a plurality of capacitors, a power supply circuit arrangement comprising a source of unregulated D-C voltage, a thyratron switching device, circuit means including conductors arranged to connect one plate of each of said capacitors to a irst terminal of said source and, a plurality of diodes arranged to connect separately the other plate of each capacitor of said plurality of capacitors to a first terminal of said switching device, control means coupled to said switching device to initiate the conduction of said switching device at a xed moment of a printing cycle, a second terminal of said source which supplies an unregulated voltage greater than said predetermined voltage, said switching device including a rst solid thyratron having first and second current carrying terminals, an inductor connecting one of said current carrying terminals of said thyratron to said second terminal of said source, a common conductor connected to all of said diodes and through a resistor to the other of said current carrying terminals of said thyratron, a refer ence voltage supply means supplying a xed reference voltage, and a voltage comparator device adapted and connected to compare a voltage derived from the voltage of said common conductor, varying during charging of said capacitors, with said fixed reference voltage and for supplying a control signal to said switching device, which signal cuts off said thyratron by a reactive action from said inductor, in order to interrupt the charging of said print capacitors as soon as the voltage of said common conductor becomes equal to said predetermined voltage.

References Cited UNITED STATES PATENTS DONALD D. FORRER, Primary Examiner HAROLD A. DIXON, Assistant Examiner U.S. Cl. X.R. 

